Sea level rose 60 percent faster than UN projections, study finds

A recent study published in the journal "Nature" suggests the U.S. may experience a 5-foot rise in sea level given all of the fossil fuel that has already been burned. NBC's Anne Thompson reports.

Projections for sea level rise in coming decades could be too conservative, experts warned Wednesday, saying they found that the rise over the last two decades is much more than predicted by the U.N. scientific body tracking climate signals.

In a peer-reviewed study, the experts said satellite data show sea levels rose by 3.2 millimeters (0.1 inch) a year from 1993 to 2011 — 60 percent faster than the 2 mm annual rise projected by the U.N.'s Intergovernmental Panel on Climate Change for that period.

"This suggests that IPCC sea-level projections for the future may also be biased low," the team wrote in the journal Environmental Research Letters.

The experts also said the IPCC was just about spot on with its predictions for warming temperatures.

"Global warming has not slowed down or is lagging behind the projections," lead author Stefan Rahmstorf, a researcher at Germany's Potsdam Institute for Climate Impact Research, said in a statement. "The IPCC is far from being alarmist and in fact in some cases rather underestimates possible risks."

The experts added that the faster sea level rise is unlikely to be caused by a temporary ice discharge from Greenland or Antarctica ice sheets because it correlates very well with the increase in global temperature.

The IPCC earlier estimated that seas rose by about 7 inches over the last century, and its most recent report, published in 2007, estimated a range of between 7 and 23 inches this century — enough to worsen coastal flooding and erosion during storm surges.

But the IPCC report did not factor in a possible acceleration of the melt of the Greenland and Antarctic ice sheets.

The IPCC "assumed that Antarctica will gain enough (ice) mass" to compensate for Greenland ice loss, the new study's authors noted, but more recent studies have shown that "the ice sheets in Greenland and Antarctica are increasingly losing mass."

Rahmstorf told Reuters his best estimate for sea level rise was between 20 inches and three feet this century, possibly more if greenhouse gas emissions of carbon dioxide surged.

In the past century, as the climate has warmed, sea level rise has accelerated. Scientists predict it will only increase, and they're studying changes in the ocean and land to better understand how and why the water is rising. NBC's Anne Thompson reports for "Changing Planet," produced by NBC Learn in partnership with the National Science Foundation.

The IPCC chair, addressing delegates to international climate talks being held in Doha, Qatar, on Wednesday made note of the recent findings on ice loss and sea level rise.

The next IPCC report, Rajendra Pachauri promised, will have "a better appreciation of mass loss of the large ice sheets of Greenland and Antarctica."

When the next IPCC report comes out in March 2014, he added, expect "a more quantitative understanding of ongoing sea level rise" — and an entire chapter on the topic.